Application of Well Control Technology to Drilling Problems in the Delaware Basin

Abstract

Abstract Wells drilled to test deep Devonian or Ellenburger formations in the Delaware Basin will encounter 5 to 7,000 ft of abnormally pressured Wolfcamp and Pennsylvanian formations. These formations contain many gas bearing sections which require mud weights from 12 to 16.7 lb/gal to balance. Frequently, these gas bearing formations are noncommercial, but of sufficient volume to be troublesome if not controlled. Since drilling with mud weights which overbalance formation pressures is inherently expensive, a great incentive exists to utilize techniques for controlling these formations with as light mud weights as possible. Successful use of light mud weights to drill Wolfcamp and Pennsylvanian formations requires a knowledge of the detection, interpretation and control of gas in the annulus. This paper discusses these aspects of well control procedures and proposes many cost-saving features that may be incorporated into drilling programs which utilize reliable well control procedures. Introduction A knowledge of well control procedures is essential to conducting a safe drilling operation. Protection of life and property is dependent on the ability to control a threatened blowout. However, if the ability to control a threatened blowout reaches a certain stage of accomplishment, then it is possible to effect major changes in a drilling program - all designed to reduce drilling costs. The need for reliable well control procedures has been receiving increased attention in the past few years.1-3 Recent advancements in drilling technology1-6 have pinpointed mud weight as the major variable in an attempt to reduce drilling costs. The major conclusion drawn is to keep mud weight as light as possible to achieve minimum drilling costs. To effect this recommendation requires an accomplished well control program. Many adverse things can occur while killing a well. The most costly item is loss of circulation and/or stuck drill pipe. A secondary concern is suspension of drilling operations while controlling the well. Minimum drilling costs cannot be achieved if the cost of adverse items outweigh benefits derived from drilling with light mud weights. The purpose of this paper is to reiterate those factors which are necessary to achieve reliable well control and to propose certain drilling procedures that can be achieved with a sophisticated state of well control. Prior to the publication of O'Brien and Goins1 in 1960, virtually all articles on well control technology were restricted to discussions about blowout prevents and how to avoid blowout conditions through crew training. O'Brien and Goins were the first to go beyond the statement "put the well on a choke and raise the mud weight". The next significant contribution to well control technology was made by Records in 1962.2 Using the concept of maintaining a constant bottom-hole pressure, Records presented a calculation procedure for determining the rate at which to expand the gas as it was circulated up the annulus. Records' contribution was doubly significant in that he also designed a specialized piece of equipment7 for precision control of surface pressure which regulates pressure directly rather than indirectly through volume control. A more recent publication by Schurman and Bell3 proposes an approximate method for a more rapid determination of the back-pressure schedule to be used to control gas expansion in the annulus. After describing their procedure, they made the statement, "The results (well control) depend strongly on the experience and understanding of the (choke) operator." This statement is equally applicable to any subject; but in the field of well control, inexperience and misunderstanding often result in a catastrophe.